This invention relates to lighting control systems, and more particularly to electronic control apparatus for controlling the intensity of electric lamps for illumination control on television and theatrical stages, or in similar applications where accuracy as well as specialized control are required to effect predetermined lighting cues.
Lighting control apparatus is known, from U.S. Pats. Nos. 3,397,344 and 3,816,797 for example, wherein the transfer characteristic of the dimmer control circuit provides a fixed relationship between a low power direct current control signal and the light output, the transfer characteristics of the circuit described in the latter patent being adjustable so that the relationship between control signal and light output can be readily altered to satisfy the somewhat different requirements of theater and television applications. In the circuit of U.S. Pat. No. 3,816,797, the transfer characteristic is determined primarily by a pair of transistors, the degree of conductivity of which controls the time required for a capacitor to charge to a value which will trigger a unijunction transsiter, thereby to determine the delay period in each half cycle of the line voltage at which time the unijunction transistor will trigger. These active elements, that is, the two transistors and the unijunction transistor, as well as their associated circuit components, being subject to some variation from component to component, the extent to which the parameters of the components of one dimmer channel match the parameters of corresponding components of other channels determines how well the performance from one channel to another is matched. In other words, unless the active components in two channels are carefully matched, even if the same direct current control signal is applied to both, the effect on the lamps being controlled may not be the same, an obviously undesirable result.
Another disadvantage of the U.S. Pat. No. 3,816,797 control circuit is that it requires for its operation two sixty cycle transformers and one pulse transformer; since one of the control circuits is required for each dimmer channel, of which there may be a hundred or more in a given installation, the control system for a large installation obviously would be bulky and relatively costly.
It is a general object of the present invention to provide an improved dimmer control circuit for controlling the intensity of large electric lamps that is more compact, dissipates less heat, and is less costly to manufacture than dimmer control circuits heretofore available.
Another object of the invention is to provide a dimmer control system for controlling a plurality of lamps on a dimmer per lamp basis wherein the performance of the several channels is matched and is not significantly affected by the parameters of the circuit components.